The phenomenon of color change in a particular material caused by an electrochemical reaction is called "electrochromism." Since the discovery of the electrochromic phenomenon in tungsten oxide, amorphous WO 3 is the most widely studied electrochromic material. Until now, WO 3 remains the most promising candidate for electrochromic devices. Electrochromic devices can switch between two optical states (colored/bleached) by injection/extraction of ions and electrons, based on the modification of transmittance and reflectance that are induced by an applied external voltage. In this study, tungsten oxide (WO 3-x ) thin films were deposited onto an ITO-coated glass substrate by reactive facing-target sputtering, and their electrochromic properties studied as a function of film thickness. The X-ray diffraction patterns reveal the amorphous properties of all the WO 3-x thin films prepared in this study. Of all the different samples prepared in this study, WO 3-x thin film of thickness 500 nm exhibited the maximum coloration efficiency of 37.3 cm 2 /C.

WO3-x thin films were deposited on induim tin oxide (ITO) glass substrates with various oxygen flow ratios from 0.55 to 0.7 by the reactive facing-target sputtering method, at a power density of 4 W/cm2 and room temperature. The structural properties of the WO3-x thin films were measured by X-ray diffractometry and Raman spectral analysis. As-deposited WO3-x thin films had an amorphous structure. In the Raman spectra, WO3-x thin films exhibited two strong peaks at 770 and 950 cm-1 attributed to the vibrations of W6+–O and W6+=O bonds, respectively. The electrochemical and optical properties of WO3-x thin films were measured by cyclic voltammetry and UV/vis spectrometry. The results showed the highest charge density at an oxygen flow ratio of 0.7 and the highest transmittance in the visible range. The maximum coloration efficiency was 30.82 cm2/C at an oxygen flow ratio of 0.7.

Tungsten oxide thin films for an electrochromic (EC) device were deposited at an oxygen flow ratio [O 2 /(Ar + O 2 )] of 0.7 using reactive facing-target sputtering with a variable working pressure. The correlation between the WO 3-x thin films and EC properties was investigated. The films structural properties were measured by X-ray diffraction; the indium tin oxide diffraction peak was observed in all the films. The electrochemical and optical properties were measured by cyclic voltammetry and UV/Vis spectrometry. The WO 3-x thin film obtained at 0.13 Pa displayed a maximum coloration efficiency of 31.42 cm 2 /C, which indicated superior EC properties.